1. Field of the Invention
The invention relates to the field of digital watermarks, and more particularly, to the use of watermarks for the secure distribution of digital data.
2. Description of the Related Art
With the recent growth of networked multimedia systems, techniques are needed to prevent (or at least deter) the illegal copying, forgery and distribution of media content, such as digital audio, images and video. Many approaches are available for protecting digital data; including encryption, authentication and time stamping. It is also desirable to determine where and by how much the digital data has been changed from the original.
One way to improve a claim of ownership over digital data, for instance, is to embed a low-level signal or structure directly into the digital data. For example, a digital watermark uniquely identifies the owner and can be easily extracted from the digital data. If the digital data is copied and distributed, the watermark is distributed along with the data. This is in contrast to the (easily removed) ownership information fields allowed by the MPEG-2 syntax.
Modern digital processing techniques can be used maliciously to remove or replace visible watermarks in digital images or video. To overcome such a problem invisible digital watermarks have been proposed. However, these invisible digital watermarks have not been able to satisfy all the requirements identified by the Society of Motion Picture and Television Engineers (SMPTE) DC28.4 group.
This group recommends that watermarks be robust (difficult to remove without greatly degrading the quality of the content), secure (difficult to detect and remove), and efficient (embedding must fit into the distribution process chain without adding unacceptable delay) to be of real value as a deterrent to piracy.
Existing approaches have been vulnerable to at least one of the following processing techniques: lossy compression up to a level that does not produce visible image degradation; specialized filters; scaling, rotation, cropping, image/frame reflection, extraction, reflection, or a combination thereof.
Regardless of the merits of prior art methods, there is a need for improved watermarking techniques for digital data that prevents copying, forgery and distribution of media content. The present invention satisfies this need.